The retry policy calculation is performed up to the MaxRetryCount property value, and each calculation follows a staggered exponential curve.

If possible, you should change the OperationTimeout value to control how long each retry should wait, rather than supplying a custom RetryExponential policy instance. The default policy RetryPolicy.Default already uses a Microsoft.ServiceBus.RetryExponential instance with a reasonable default value that interacts with the operation timeout value.